Method for separation of aluminium oxide from raw material



Patented Aug. 25, 1936 A um'rs STATES PATENT OFFICE Karl Helge Sigfrid Liifquist,Stockholm Sweden No Drawing.

Serial No. 53,271. 1934 Application December 6, 193,5,

In Sweden December 10,

16 Claims. (01-. 23- 142 7 This shows that the A1203-crystals had been sep- The present invention considers a method for separation of aluminium oxide, A1203, from raw material, which besides A1203 contains mainly one or several of certain acid oxides, that means oxides, which are able to form salts with basic oxides, as for instance silicium dioxide, S102 and titanium dioxide, T102, by forming a melt in which after freezing A1203 occurs mainly in the form of grains .or crystals of free A1203, while the acid oxide 'or oxides as for instance Si02 and/or T102 are chemically combined with a basic oxide, that means in the examples given as silicate or titanate, whereupon A1203 is separated from the solidified melt by means of some separation process, as for instance gravity concentration or flotation. Chemical decomposition of the ground mass can also be used for separating this mass from A1203.

Such a melt is obtained according to the present invention by melting the raw material containing A1203 together with a certain amount of lead oxide, PbO, or some lead salt which on melting will give PbO, e. g. lead carbonate, PbO-COz, which by heating gives off C02 and forms PbO. By melting experiments made by me it was namely found that if a certain minimum amount of PbO is used in the melt its content of S102 combines with PbO, forming Pb-silicate, and further that T102 occurring, combines with PbO, forming Pb titanate, while on the contrary A1203 does not form any stable compound with PbO nor does it combine with $102 to form Al-silicate, but on cooling and solidifying of the melt A1203 is separated in the form of grains or crystals of free It is to be remarked, however, that, as already mentioned, a certain minimum. amount. of PbO is required in order really to obtain A1203 in the form of free A1203. By melting experiments made by me the following has been found regarding this amount of P100 required for a certain charge of A1203 and S102.

According to the amount of added P190 in: relation to the amount of S102 occurring, difierent silicates as Pb0.Si02, 2Pb 0.Si02 and (though less stable) 4 PbO.Si02 may be formed. Thus, in one case with a melt containing PbO, 16% A1203 and 4% S102 crystals of the silicate 2Pb0.Si02 were obtained together with a certain amount. of free PbO and crystals of A1203. The melting began at a temperature of 700 C. and the maximum temperature used was 900 C. when the whole charge was. well molten. It also proved that the A1203-crystals. were enriched towards the upper part of the melt, if it was left to cool slowly.

arated from themelt before it had solidified completely, and thereby, on account of their lower density, had risen in the, heavier molten Pb-silicate. 15% A1203, and 25% S102, the amount of added PbO was smaller than thatwhich wasrequired for binding the whole amount of S102 to silicate, as it was found that part of S102 combined with a stoichiometric amount of A1203 aluminium silicate. 3Al203:2Si02. or :possibly A1203-.Si02;and'besides that some free S102 was obtained. r

Therefore, in order to obtain the whole amount of A1203 in afree form the amount of added PbO should be' at least 'solarge that the whole amount of S102 combines into Pb-silicate, thatmeans the ratio Pb0:Si02*must be at leastas large as it is given by the formula Pb0.S102. In order toobcontains mainly S102 and T102 is melted with the 1 minimum amount of Pb0'stoichiometrical1ycalculated as described, free A1203 will be formed in the cooling melt, while S102 and T102 form Pbsilicate and Pb -titanate respectively.

The composition of the charge may however 1 preferably be restricted-'also in regard to its content ofi'Al2 03. It was namely found that with increasing percentages of A1203 the temperature which is required for melting increases very rapidly, and with increasing temperature PbO evaporates strongly, which causes losses of P before the charge is quite molten, or even it will make a homogeneous melting very difficult. On account of that the 'conten'tof'Al203 in the charge should preferablynot'exceed about 35 which corresponds to a-melting' temperature of approximately somewhat more than 1000" 0., slightly varyingalso withthe content of S102.

As an example may be mentioned that a quiet and good melting without any losses worth mentioning of PbO was obtained at 900 C. with a charge consisting of 80% PbO, 16% A1203 and 4% S102, while: another charge with 30% A1203 gave perceptible-losses of Pb0 at a melting temperatur us doia out 1I00 C.

In another melt, containing 60% PbO,

to form Considering the molecular weights of Pb0=223 and of Si02=60, the composition of a melt containing mainly PbO, A1203 and $102, which will give a good melting without high vapour-losses of Pb0, and with separation of free A1203 on cooling, will be determined by the following conditions.

The weight content of PbO shall be at least 223/60=3.8 times the content of S102, or, better, at least 2X223/60=7 .6 times the content of S102, and the weight content of A1203, ought to be less than about 35%, or preferably about 1020%. A mean value for the PbO-content of at least about 5 times the content of S102 may also be used. By means of these figures the weight content of PbO needed for any charge of A1203 and. S102 may be calculated, as will be shown by an example. A material containing A1203 and 20% S102 is given. For parts of that material is required at least 3.8 20='76 parts of PbO, or preferably at least 7.6X20=l52 parts of P110. The mixtures content of A1203 will in the first case be and in the second case Thus, in the first case the content of A1203 is too high, and in the second case it is just about the described upper limit of 35%, mentioned above. By adding some further amount of PhD or PbO- rich silicate, easily calculated, the A1203 content can be lowered, for instance down to 10-20% so as to give a charge of a suitable low melting point, as described in the foregoing.

For T102 a' similar stoichiometric calculation can be made. Considering the molecular weight of Ti02=80, the amount of PhD required for binding T102 will be at least 223/80=2.8 times the weight-amount of T102 (or better 2 223l80=5.6 times the weight amount of T102) A mean value of at least about 4 times the T102 content may also be used. When S102 and T102 'occur together the amounts of PbO required for each of them are to be summarized. Stoichiometrically. one part by weight of T102 is equivalent to part of S102, which may be used for facilitating the calculation of the amount of Pb0 required.

For separating A1203 as far as possible in a quantitative Way from the acid oxides S102 and T102 the melt should not contain any appreciable amount of other basic oxides as FeO, CaO, MgO, Na2O, K20 because such oxides, in the presence of A1203, are able to form aluminates and if S102 also be present, they are able to form silicatealuminates, which of course implies a decrease of the amount of free A1203. Therefore, if such oxides occur in the raw material to be treated their amount should preferably be decreased before melting with PbO, by some preliminary treatment of the raw material. Such removal is not necessary however, but is to be preferred as it will result in a higher yield of A1203.

An application of industrial importance of this method is the recovery of A1203 from certain raw materials, occurring in nature, for the production of Al. Other ranges of application also occur, as will be mentioned in the following.

Raw materials occurring in nature containing Al203, which are suitable for treatment by this method are primarily bauxites, clays and latherites. Besides A1203, S102, T102 and H20 these materials contain only Fe203 in some appreciable amount. Fe203 can be removed almost completely by means of several known processes amongst which may be mentioned reduction to FeO, followed by leaching with acid, reduction to E2304 and magnetical separation, or removal in chlorine gas. The hydrate water can be removed as vapour by heating to at least 600 C. It may be mentioned that T102 can be removed by some similar preliminary treatment as for instance in a stream of chlorine gas, according to what is already known.

A dark, that means Fe203-rich bauxite, of the analysis 58% A1203, 3% S102, 13% H20, 23% Fe2O3, 3% T102 may be assumed. After removing Fe and H20 as has been described the material will consist of 91% A1203, 4.5% S102 and 4.5% T102. This charge is mixed with PbO in sufficient amounts to combine with S102 and T102 to form Pb0.Si02 and Pb0.Ti02, or, better, so that 2Pb0.Si02 and 2Pb0.T102 are formed. As however in this case the content of the refractory substance A1203 is high as compared with the content of S102 a certain amount of PhD or Pb-silicate is added besides the stoichiometrically calculated amount of PhD so that the content of A1203 will be about 10-20% and the total amount of PbO will be of the order of magnitude 70-80%. After melting together at a temperature of 800-900 C. the melt is left to cool slowly in moulds, whereby relatively large crystals of A1203 are obtained in a ground mass of PbO, Pb-silicate and Pb-titanate.

For facilitating the enrichment of the lighter A1203 towards the top of the melt, a slow cooling by which A1203 falls out of solution can be followed by a rapid heating when A1203 rises in the liquid mass. This cooling and heating can be made in the moulds or even in the melting furnace. used. centrifuging of the melt can also be used. After crushing, the lighter A1203 is separated from the heavier Pb-compounds for instance by means of some gravity concentration process, or eventually by flotation.

The recovery of PbO, which is of importance for the economy of the process, can be made in different ways, as for instance chemically by leaching the ground mass containing Pb-silicate and Pb-titanate with certain acids, giving Pbsalts, from which PbO and the acid used are recovered. Also metallurgical recovery of PbO by reduction to Pb and subsequent oxidation to PbO can be used. T102 can be recovered from the Pb-titanate by different chemical or metallurgical methods.

For the separation of A1203 from S102 formed at the chemical decomposition of the silicate, in

composition in acid of the Pb-silicate-titanate mixture and treating the mixture S102 and T102 with molten Pb-acetate. In this Way S102 and T102 can be obtained in free form in separate fractions as by-products.

A1203 obtained by this method can be used for the production of Al in already known methods,

:by electrolysis of molten A1203. It might also be In orderto'lower the melting temperature and the viscosity of the charge addition can be. made of substances which are soluble in the melt without having any chemical influence on- A1203. Such substances are for instance certain sulphides as F08 and CuzSas has been proved by melting experiments made by me. Also haloides of Pb and PbC12 might be used.

Having now described my invention, what I claim as new and desired to secure by Letters Patent is:

1. The process of separating aluminium oxide from raw material, containing besides aluminium oxide mainly silicium dioxide, comprising forming a melt containing the raw material and lead oxide in such amounts that the weight content of lead oxide is at least 3.8 times the content of silicium dioxide, cooling the melt slowly and separating the grains of aluminium oxide formed in the cooling melt from the siliceous ground mass.

2. The process of separating aluminium oxide from raw material, containing besides aluminium oxide mainly silicium dioxide, comprising forming a melt containing the raw material and lead oxide in such amounts that the weight content of lead oxide is at least 7.6 times the content of silicium dioxide, cooling the melt slowly and separating the grains of aluminium oxide formed in the cooling melt from the siliceous ground mass.

3. The process of separating aluminium oxide from raw material, containing besides aluminium oxide mainly silicium dioxide, comprising forming a melt containing the raw material and lead oxide in such amounts that the weight content of lead oxide is at least 3.8 times the content of silicium dioxide and the weight content of aluminium oxide less than about 35%, cooling the melt slowly and separating the grains of alumininum oxide formed in the cooling melt from the siliceous ground mass.

4. The process of separating aluminium oxide from raw material, containing besides aluminium oxide mainly silicium dioxide, comprising forming a melt containing the raw material and lead oxide in such amounts that the weight content of lead oxide is at least 7.6 times the content of silicium dioxide and the weight content of aluminium oxide less than about 35%, cooling the melt slowly and separating the grains of aluminium oxide formed in the cooling melt from the siliceous ground mass.

5. The process of separating aluminium oxide from raw material, containing besides aluminium oxide mainly titanium dioxide, comprising form ing a melt containing the raw material and lead oxide in such amounts that the weight content of lead oxide is at least 2.8 times the content of titanium dioxide, cooling the melt slowly and separating the grains of aluminium oxide formed in the cooling melt from the ground mass.

6. The process of separating aluminium oxide from raw material, containing besides aluminium oxide mainly titanium dioxide, comprising forming a. melt containin the raw material and lead oxide in such amounts that the weight content of lead oxide is. at least, 5.6: times. the content of titanium dioxide; cooling the melt slowly and separating the grains of aluminium oxide formed in the cooling melt from theground mass.

'1". The process. of separating aluminium oxide from raw material, containing besides aluminium oxide mainly titanium dioxide, comprising forming a melt containing the raw material and lead oxide in such amounts that the weight content of lead oxide is at least 2.8 times the content of titanium dioxide and the weight content of aluminium oxide less than about 35%, cooling the V melt slowly and separating the grains of aluminium oxide formed in the cooling melt from the ground mass. 7

8.. The process of separating aluminium oxide from raw material, containing besides aluminium oxide mainly titanium dioxide, comprising forming a melt containing the raw material and lead oxide in such amounts that the weight content of lead oxide is at least 5.6 times the content of titanium dioxide and the weight content of aluminium oxide less than about 35%, cooling the melt slowly and separating the grains of aluminium oxide formed in the cooling melt from the ground mass.

9. The process of separating aluminium oxide from raw material, containing besides aluminium oxide mainly silicium dioxide and titanium dioxide, comprising forming a melt containing the raw material and lead oxide in such amounts that the weight content of lead oxide is at least 3.8 times the content of siliciiun dioxide plus 2.8 times the content of titanium dioxide, cooling the melt slowly and separating the grains of aluminium oxide formed in the cooling melt from the ground mass.

10. The process of separating aluminium oxide from raw material, containing besides aluminium oxide mainly silicium dioxide and titanium dioxide, comprising forming a melt containing the raw material and lead oxide in such amounts that the weight content of lead oxide is at least 7.6 times the content of silicium dioxide plus 5.6 times the content of titanium dioxide, cooling the melt slowly and separating the grains of aluminium oxide formed in the cooling melt from the ground mass.

11. The process of separating aluminium oxide from raw material, containing besides aluminium oxide mainly silicium dioxide and titanium dioxide, comprising forming a melt containing the raw materal and lead oxide in such amounts that the weight content of lead oxide is at least 3.8 times the content of silicium dioxide plus 2.8 times the content of titanium dioxide and the weight content of aluminium dioxide less than about 35%, cooling the melt slowly and separating the grains of aluminium oxide formed in the cooling melt from the ground mass.

12. The process of separating aluminium oxide from raw material, containing besides aluminium oxide mainly silicium dioxide and titanium dioxide, comprising forming a melt containing the raw material and lead oxide in such amounts that the weight content of lead oxide is at least 7.6 times the content of silicium dioxide plus 5.6 times the content of titanium dioxide and the weight content of aluminium oxide less than about 35%, cooling the melt slowly and separating the grains of aluminium oxide formed in the cooling melt from the ground mass.

13. The process of separating aluminium oxide from raw materiaL'containin besides aluminium oxide mainly silicium dioxide and/or titanium dioxide by forming a melt containing the raw material and lead oxide, comprising a slow cooling of the melt for separation of grains of aluminium oxide followed by a rapid heating for flotation of these grains towards the upper surface of the melt.

14. The process of separating aluminium oxide from raw material, containing besides aluminium oxide mainly silicium dioxide and/ or titanium dioxide by forming a melt containing the raw material and lead oxide, comprising a slow cooling of the melt for separation of grains of aluminium oxide, followed by a rapid heating and centrifuging of the melt for accelerated separation of these grains.

15. The process of separating aluminium oxide 'from raw material, containing besides aluminium oxide mainly silicium dioxide by forming a melt containing the raw material and lead oxide and cooling the melt slowly, comprising treating the cooled and crushed melt with acetic acid so as to form lead acetate and a mixture of aluminium oxide and silicium dioxide, and melting the lead acetate whereby aluminium oxide sinks to the bottom, and silicium dioxide rises towards the surface of the molten acetate.

16. The process as claimed in claim 15, comprising treating the cooled and crushed melt with some acid which dissolves lead oxide and melting the residue of aluminium oxide and silicium dioxide with lead acetate.

KARL HELGE SIGFRID LOFQUIST. 

